1. Technical Field
Overcoating compositions for photoresist and methods for reducing linewidth of the photoresist patterns are disclosed. More specifically, an overcoating composition containing acids is coated on a whole surface of a photoresist pattern formed by a common lithography process to diffuse the acids into the photoresist pattern. The regions of photoresist pattern where the acids are diffused are developed with an alkali solution to be removed. As a result, the linewidth of positive photoresist patterns can be reduced, and the linewidth of negative photoresist patterns can be prevented from slimming in a subsequent linewidth measurement process using SEM.
2. Description of the Related Art
Conventionally, exposure energy has been increased to reduce linewidth of photoresist patterns.
However, although the above method is very effective to reduce the linewidth of photoresist patterns, the amount of light diffracted according to increase of the energy becomes larger as shown in FIG. 1. As a result, a portion of the photoresist pattern is removed (10), and the photoresist pattern 20 is transformed with a triangle type. Also, the thickness of the photoresist pattern 20 is reduced.
The triangular profile and the reduction of resist thickness degrade subsequent etching processes. Specifically, when the linewidth of the pattern is measured, the triangle-type pattern degrades reproducibility, and is transcribed into lower films to transform subsequent etching patterns into triangle-types. As a result, resistance increases.
The reduction of resist thickness disables a mask function on plasma in a process of etching lower films. As a result, etching patterns are transformed and broken.
When negative photoresist patterns are formed, a SEM measurement is performed by setting a critical dimension (hereinafter, referred to as ‘CD’) target. The CD soon after the SEM measurement is almost identical with the target. However, in 10 minutes after the SEM measurement, the pattern CD decreases due to electronic beam of high energy generated in photoresist composition during the measurement process.
The pattern CD more decreases due to far ultraviolet light sources such as ArF (193 nm) and VUV (157 nm) in the semiconductor manufacture for ultrafine high integration.
Most photoresist compositions for 193 nm and 157 nm which satisfy various physical properties such as low light absorbance, high etching, excellent substrate adhesiveness, transparency to light sources and development capability in alkali developers do not include aromatic materials which alleviate electronic beams of high energy generated from the SEM measurement process. As a result, the pattern CD decreases.
The pattern CD more decreases due to accelerating voltage of electronic beams and exposure time as patterns become smaller, which result in a degradation of the yield for the process.